I'm glad to see that you're planning on 3 days and not 2, and that you're planning a very early start. That should make your trip safer and easier. Just remember that preparing breakfast and breaking camp, in the dark, may take longer than you think if you have not done it before. And with that many inexperienced folks in your party someone may take a very long time. Or someone may want to sleep in. You can't hit the trail until everyone is ready. Your planned 4 AM start could easily turn into a 5 AM start. The best laid plans on paper sometimes don't translate into reality. Believe me I've been there.

One more factor not mentioned yet is the elevation. The South Rim is about 6600' and the North Rim is about 1000' higher. This is not terribly high but it is much higher than Florida. Thinner air affects everyone differently. You said you don't all have mountain experience. The altitude may affect you very little or it may have a profound effect on you or someone in your party. Be prepared for that.